“How many times are you going to throw that at me?” Shireen shouted. “I know I was the one who talked you into coming here. I know it was a mistake. Now’s our chance to fix it.”

Rachel opened her mouth to give another angry reply, then something seemed to break. All of a sudden she just looked tired and miserable. “It’s too late.” Rachel sounded desperately unhappy, and just for an instant I wondered if this had been how she’d always felt. “Everything we’ve done . . . Who’s going to want an ex–Dark apprentice? We have to stick it through. It’s the only way we’re going to be safe.”

“We’re never going to be safe, Rach,” Shireen said gently. Her anger was gone too; she only looked sad. “And that’s our fault. I know you want me to stay and help you with Tobruk. But after Tobruk there’d be someone else and someone else. As long as we live as Dark mages there’ll always be another Tobruk. The only way to get away from them is to leave.”

Rachel hesitated, and for the first time I had the feeling she was really wavering. Shireen put her hands on Rachel’s shoulders, and this time Rachel didn’t push her away. “Listen to me,” Shireen said, looking straight into Rachel’s eyes. “We might have made bad choices, but we don’t have to keep making them. We can turn back, if we admit we were wrong and start fixing our mistakes. I can’t undo what we’ve done but I can help Catherine right now. And that’s what I’m going to do.” Shireen moved Rachel to the side and started walking towards the archway leading to the cells.

Rachel stared after her for a second, then fright leapt into her eyes. “No! Don’t!”

“It’s the only way, Rach.”

“You can’t do this!” Rachel’s voice rose, broke. “He’ll kill me! You’re supposed to be on my side!”

Shireen didn’t stop or turn; she was passing the altar. “Stop!” Rachel shouted. Her hand began to lift, blue-green light flickering around it. Shireen didn’t react. “Stop!” Shireen kept walking. “Stop!” And a thin blue-green ray flashed from Rachel’s hand, striking Shireen’s lower back and passing through into the archway beyond.

Shireen stumbled and stopped. She turned and looked at Rachel in complete surprise, then her legs gave out from underneath her and she crumpled to the stone.

Rachel stood frozen, her hand still raised. “I didn’t—” she began. “I didn’t mean to—”

Shireen stared at Rachel for a long moment, then a kind of realisation crept into her eyes and she leant her head back against the stone. “Oh,” she said quietly.

“Oh God, you’re bleeding.” Rachel looked around wildly. “Just stay there. I’ll get you something, I’ll—”